Chapter 4 Wireless LAN Technologies and Products 3122021

Chapter 4 Wireless LAN Technologies and Products 3/12/2021 Prof. Huei-Wen Ferng 1

General Description Overview of Technologies 3/12/2021 Prof. Huei-Wen Ferng 2

Technology Trends n n n Physical layers of WLAN are based on SS (FHSS and DSSS) and IR technologies Frequency bands: ISM band Date rate: • Current products/standards: 1~54 Mbps • Future: 100 Mbps and above 3/12/2021 Prof. Huei-Wen Ferng 3

Wireless LAN Wish List n High speed • At least as fast as today’s Ethernet n Low cost • Not much more than today’s Ethernet n Coverage • Throughout the building or campus n n n n No use of the battery of the mobile computer, or at least minimal impact No interference with other equipments Easy installation, use, and management Easy repair and upgrading PCMCIA form factor No external antenna Co-operability of different wireless LAN systems 3/12/2021 Prof. Huei-Wen Ferng 4

Effect of Multi-path Fading n n Multi-path: a number of different paths of signals arrives at the receiver Signals of different propagation delays can degrade performance 3/12/2021 Prof. Huei-Wen Ferng 5

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Network Architecture 3/12/2021 Prof. Huei-Wen Ferng 8

Network Architecture (Cont’d) n Infrastructure • Connectivity is accomplished by access point (AP) between a station and other station or network n Ad-hoc network • This network is set up temporarily to meet some immediate need • It has no centralized server, like AP 3/12/2021 Prof. Huei-Wen Ferng 9

MAC Protocols n Three MAC protocols for wireless LANs • Listen Before You Talk MAC protocol • Integrated wireless LAN MAC protocol • Polling MAC protocol 3/12/2021 Prof. Huei-Wen Ferng 10

Listen Before You Talk MAC protocol n n LBT is basically a non-persistent CSMA protocol It differs from CSMA in two ways • An RTS packet is transmitted before data is transmitted to the receiver, then the receiver transmits a CTS packet to be heard by all nodes to grant data transfer from the sending node • After RTS/CTS packets, the sending node transmit the data n LBT or RTS/CTS scheme avoids the hidden node problem 3/12/2021 Prof. Huei-Wen Ferng 11

Integrated CSMA/TDMA MAC Protocol n n A hybrid of reservation and random access The frame is segmented into • Two reservation intervals for isochronous Traffic • One interval for random access traffic n Movable boundary by a control function • Infrastructure: by AP • Ah-hoc: the function is distributed among the nodes 3/12/2021 Prof. Huei-Wen Ferng 12

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Contents of Headers n Header AH: • Length of TA, TB, TC • BSID: Unique ID of the AP • NET_ID: Network ID • NEXT_FREQ/NEXT_CODE/NEXT_CHNL • <Si, Wi>: AP transmit Si packets to user Wi 3/12/2021 Prof. Huei-Wen Ferng 14

Contents of Headers (Cont’d) n Header BH: • The length of TB, TC • <Si, Vi, Wi>: User Vi transmits Si packets to user Wi n Header CH: • The length of TC • K: current estimate of users attempting transmission in random access section 3/12/2021 Prof. Huei-Wen Ferng 15

Polling MAC Protocol n Incorporate the fairness issue • E. g. , stock trading application n Mechanism • A node has a packet to send, it first sends a request to the control point • The control point polls the users in turn by referencing the request queue • Data needs ACK and goes through an AP, therefore, no ad-hoc networking 3/12/2021 Prof. Huei-Wen Ferng 16

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Power Management n n In order to achieve low power budgets, the WLAN adaptor must sleep as much as possible Three States are defined for WLAN adapter: • Transmit state n Transmitter is turned on • Awake state n Receiver is powered on and ready to receive • Doze state n 3/12/2021 Transceiver dozing Prof. Huei-Wen Ferng 18

Power Management (Cont’d) n n n The power savings scheme is with the help of AP The AP buffers traffic for dozing nodes The AP informs nodes of traffic in broadcast packets called Traffic Delivery Information Messages (TDIM) • The frame header include: which stations have data to receive, how much data to receive, and when it will be delivered 3/12/2021 Prof. Huei-Wen Ferng 19

Power Management (Cont’d) n The node will wake up when • • • n n they are transmitting they have data to receive in the specify time during the frame header to check the TDIM The node periodically check the frame header Palm-top computer do not wake up every frame. They remain sleep as long as they wish 3/12/2021 Prof. Huei-Wen Ferng 20

Interconnection with Backbone Networks n Connecting with the same network • Done below the network layer using MAC layer bridges n Mobility between different networks • Done at the network layer via new protocols such as Mobile IP 3/12/2021 Prof. Huei-Wen Ferng 21

Mobility within the Same Network n n Mobile nodes are roaming in the same area that are covered by different APs in the same network Each AP contains three components • A WLAN interface card (AP<->Node) • A wired LAN interface card (AP<>Network) • A MAC layer bridge to filter the traffic between the wireless subnet and the backbone 3/12/2021 Prof. Huei-Wen Ferng 22

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Bridges n n Bridging is used to filter traffic from different wired segments of a large LAN Differences among repeater, bridge, and router? 3/12/2021 Prof. Huei-Wen Ferng 24

Mechanism of Bridges n n n When a bridge is first installed, it acts as a repeater Then as a traffic goes through it, it learns which nodes are on which LAN segment and forms a table Next time it receives a packet, it forwards it only on the LAN segment destined; otherwise, it broadcasts on all LAN segments 3/12/2021 Prof. Huei-Wen Ferng 25

Timers n n n The entries in the table are not kept forever Bridges have a timer for each node The age-out timers in wired LANs are on the order of hours The age-out timers in wireless LANs are on the order of minutes What happen if the age-out timer is too short? What happen if the age-out timer is too long? 3/12/2021 Prof. Huei-Wen Ferng 26

Additional Functions of Bridges n n n Buffering between different speed LANs Changing frame formats between incompatible LANs Adding and deleting fields within the frame, e. g. , 802. 3 has a data length field but 820. 4 doesn’t 3/12/2021 Prof. Huei-Wen Ferng 27

MAC Layer Bridging Protocols n Spanning tree bridges • Need a distributed database of where all the nodes are and the best way to reach any node • The network topology takes shape using multiple bridges • The way to form the topology n n Using a distributed algorithm for selecting a root bridge and a tree that reaches every other bridge Source routing bridges • Rely on the source node, which keeps a table of where other nodes are • It includes the route the packet is to take in the header • Places greater burden on the nodes 3/12/2021 Prof. Huei-Wen Ferng 28

Mobility among Different Networks (Mobile IP) n The goals of mobile IP are: • • 3/12/2021 Mobility is handled at the network layer Transport and higher layers are unaffected Applications do not need to change The infrastructure of non-mobile routers are unaffected Non-mobile hosts are unaffected Continuous operation occurs across multiple networks Security is as good as with existing networks Prof. Huei-Wen Ferng 29

Mobile IP n n Briefly Speaking, to take a mobile IP address for mobility with minor changes At present, IP address is associated with a fixed network location like a phone number 3/12/2021 Prof. Huei-Wen Ferng 30

Mobile IP (Cont’d) n Terms Definition used in Mobile IP operations: • Mobile host (MH): a movable host • Home address (HA): a permanent IP address used to identify an MH anytime • Home network (HN): the logical network where an MH’s HA resides • Care of address (COA): a temporary address used to locate an MH at some particular instant 3/12/2021 Prof. Huei-Wen Ferng 31

Mobile IP (Cont’d) n n n Agents: in the routers to implement the new software offering mobile capabilities Home Agent (->HLR): An agent that redirects packet from a home network to the COA of an MH Foreign Agent (->VLR): a specialized forwarding agent that • Offers a COA • Maintains and performs mapping between the COA and HA of an MH 3/12/2021 Prof. Huei-Wen Ferng 32

Mobile IP (Cont’d) Boston San Francisco Washington Triangle routing 3/12/2021 Prof. Huei-Wen Ferng 33

Mobile IP (Cont’d) n Triangle routing • Not too bad if only one or two packets n For many packets, FA in Boston sends a message to the fixed node in Washington and asks it to use the mobile node’s COA instead its HA, the packets then go directly from Washington to Boston 3/12/2021 Prof. Huei-Wen Ferng 34

The operation of Mobile IP 3/12/2021 Prof. Huei-Wen Ferng 35

The Operation of Mobile IP (Cont’d) n How does a MH find an FA? • Through the advertisements n FAs send out service advertisements that announce their willingness to provide COA to visiting MHs • MH can send out a solicitation packet asking if a FA is in the vicinity 3/12/2021 Prof. Huei-Wen Ferng 36

Packet Types of Mobile IP n n n n Advertisement packet Solicitation packet Registration MH to FA registration packet FA to HA registration packet HA to FA registration ACK packet FA to MH registration ACK packet 3/12/2021 Prof. Huei-Wen Ferng 37

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The PCS Model for Mobility n n n In cellular and PCS networks, each person has a unique number similar to Mobile IP address This number is stored in Home Location Register (HLR) When user is visiting foreign location, he/she is automatically registered with a Visitor Location Register (VLR) 3/12/2021 Prof. Huei-Wen Ferng 39

PCS Call Flow Destination HLR (4) (3) Calling UPT user (2) Originating network Called UPT user (1) Source HLR 3/12/2021 Terminating network Authentication: (1), (2) Service profile, routing: (3), (4) Prof. Huei-Wen Ferng 40

Wireless LAN Standards n IEEE 802. 11 • IEEE n 802. 11 a 802. 11 b High-performance radio LAN (Hiper. LAN) • Hiper. LAN type 1 • Hiper. LAN type 2 3/12/2021 Prof. Huei-Wen Ferng 41

IEEE 820. 11 3/12/2021 Prof. Huei-Wen Ferng 42

Hiper. LAN n Hiper. LAN Type 1 (H/1) • A connectionless packet-based broadband WLAN standard at 5 GHz in 1996 n Hiper. LAN Type 2 (H/2) • A connection-oriented high-performance technology at 5 GHz in 2000 3/12/2021 Prof. Huei-Wen Ferng 43

Resources n ETSI/BRAN website • http: //www. etsi. org/bran 3/12/2021 Prof. Huei-Wen Ferng 44

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References n n R. A. Dayem, Mobile Data and Wireless LAN Technologies William Stallings, “IEEE 802. 11: Moving Closer to Practical Wireless LANs”, IEEE IT Pro, 2001 B. H. Walke et al. , “IP over Wireless Mobile ATM-Guaranteed Wireless Qo. S by Hiper. LAN/2”, Proc. Of IEEE, 2001 Perkins, “Mobile Networking Through Mobile IP”, IEEE Internet Computing, 1998 3/12/2021 Prof. Huei-Wen Ferng 46